Re: how to rescue this backup data (could not get original value for mkisofs -C)
在 2010-01-03日的 17:02 +0100，Thomas Schmitt写道：
> If so, then you have the task to guess the offset
> value TheOffset that was used with
>
> genisoimage -C c1,TheOffset
snip...
> This would be easy if you had the DVD from sr0.
>
> If not, then lets have a look into ECMA-119,
> 8.4 Primary Volume Descriptor:
> "[byte position counting begins with 1]
> 157 to 190
> Directory Record for Root Directory"
> 9.1 Format of a Directory Record
> "3 to 10
> Location of Extent"
>
> This value tells you where the ISO image has its
> first storage chunk for directory records.
> It is supposed to sit shortly after the start
> of the image.
snip..
> obtain the value from your image backup.iso.
> E.g.
> $ dd if=backup.iso. bs=2048 skip=16 count=1 | \
> dd bs=1 skip=158 count=4 | od -d
> 0000000 40156 21
>
> Compute the block number
> $ expr 21 '*' 65536 + 40156
> 1416412
Ariel@Jamaica:/tmp> dd if=/dev/sr1 bs=2048 skip=1256112 count=1 \
| dd bs=1 skip=158 count=4 | od -d
4+0 records in
4+0 records out
4 bytes (4 B) copied，0.122195 秒，0.0 kB/秒
0000000 46890 4864
0000004
1+0 records in
1+0 records out
2048 bytes (2.0 kB) copied，0.0360709 秒，56.8 kB/秒
Ariel@Jamaica:/tmp> expr 4864 '*' 65536 + 46890
318813994
This value surprised me a bit, it is unlikely even close to a possible
offset. Because:
Ariel@Jamaica:/tmp> expr 318813994 "*" 2 / 1048576
608
so this offset is 608GB away from beginning.
So I cannot go on from here.
Thank you very much not only by instructing me in detail but also thank
you for correctly guessed my level of background knowledge to make the
instruction not too detail nor too brief. I always appreciate someone
with communication skill like you do.
I thus doubt there are something wrong with the "superblock". I think
now what I can do is to get you dump of everything until 190, end of
volume descriptor, to see if there are something wrong. It is not
impossible that it happened to the backup operator to have typed in a
irrational value for "mkisofs -C"
Ariel@Jamaica:/tmp> dd if=/dev/sr1 bs=2048 skip=1256112 count=1 | od -cx
0000000 001 C D 0 0 1 001 \0 L I N U X
0143 4430 3031 0100 4c49 4e55 5820 2020
0000020
2020 2020 2020 2020 2020 2020 2020 2020
0000040 w w w . e e c z
2020 2020 2020 2020 7777 772e 6565 637a
0000060 . o r g . c n B a c k u p
2e6f 7267 2e63 6e20 4261 636b 7570 2020
0000100 \0 \0 \0 \0 \0 \0 \0 \0
2020 2020 2020 2020 0000 0000 0000 0000
0000120 ! _ 002 \0 \0 002 _ ! \0 \0 \0 \0 \0 \0 \0 \0
215f 0200 0002 5f21 0000 0000 0000 0000
0000140 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
0000 0000 0000 0000 0000 0000 0000 0000
0000160 \0 \0 \0 \0 \0 \0 \0 \0 001 \0 \0 001 001 \0 \0 001
0000 0000 0000 0000 0100 0001 0100 0001
0000200 \0 \b \b \0 300 002 \0 \0 \0 \0 002 300 263 * 023 \0
0008 0800 c002 0000 0000 02c0 b32a 1300
0000220 \0 \0 \0 \0 \0 023 * 265 \0 \0 \0 \0 " \0 267 *
0000 0000 0013 2ab5 0000 0000 2200 b72a
0000240 023 \0 \0 023 * 267 \0 \0 \0 \0 \0 \0 k \a
1300 0013 2ab7 0020 0000 0000 2000 6b07
0000260 036 \v 0 ' 002 \0 \0 001 \0 \0 001 001 \0
1e0b 3027 2002 0000 0100 0001 0100 2020
0000300
2020 2020 2020 2020 2020 2020 2020 2020
*
0001060 M K
2020 2020 2020 2020 2020 2020 2020 4d4b
0001100 I S O F S I S O 9 6 6 0 / H
4953 4f46 5320 4953 4f20 3936 3630 2f48
0001120 F S F I L E S Y S T E M B U
4653 2046 494c 4553 5953 5445 4d20 4255
0001140 I L D E R & C D R E C O R D
494c 4445 5220 2620 4344 5245 434f 5244
0001160 C D - R / D V D C R E A T O
2043 442d 522f 4456 4420 4352 4541 544f
0001200 R ( C ) 1 9 9 3 E . Y O U
5220 2843 2920 3139 3933 2045 2e59 4f55
0001220 N G D A L E ( C ) 1 9 9 7
4e47 4441 4c45 2028 4329 2031 3939 3720
0001240 J . P E A R S O N / J . S C H I
4a2e 5045 4152 534f 4e2f 4a2e 5343 4849
0001260 L L I N G
4c4c 494e 4720 2020 2020 2020 2020 2020
0001300
2020 2020 2020 2020 2020 2020 2020 2020
*
0001440 2 0 0
2020 2020 2020 2020 2020 2020 2032 3030
0001460 7 0 8 0 7 2 3 0 6 3 0 0 0 2 0
3730 3830 3732 3330 3633 3030 3020 3230
0001500 0 7 0 8 0 7 2 3 0 6 3 0 0 0 0
3037 3038 3037 3233 3036 3330 3030 2030
0001520 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 \0
3030 3030 3030 3030 3030 3030 3030 3000
0001540 2 0 0 7 0 8 0 7 2 3 0 6 3 0 0 0
3230 3037 3038 3037 3233 3036 3330 3030
0001560 001 \0
2001 0020 2020 2020 2020 2020 2020 2020
0001600
2020 2020 2020 2020 2020 2020 2020 2020
*
0002560 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
2020 2000 0000 0000 0000 0000 0000 0000
0002600 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
0000 0000 0000 0000 0000 0000 0000 0000
*
1+0 records in
1+0 records out
2048 bytes (2.0 kB) copied，0.0374677 秒，54.7 kB/秒
0004000
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